We can and do full body scans. Typically in the context of research, or for focus/metastasis search in current clinical settings.
The problem is that, in clinical practice, with every imaging technology there are trade-offs. Just because we see something out of the ordinary in a scan doesn't immediately tell us whether it's pathology, pathology worth investigating/treating, or if it's just a normal physiological variation.
Which means that, when "something" is seen on a scan, we must do further testing, either increasingly invasive, or increasingly time consuming and expensive.
I agree with the sentiment that if we had a way cheap, fast, and harmless way to scan an entire body we would unlock many new research areas and that it would further our medical understanding, and eventually ripen for clinical use.
However currently, I do not see any benefit in giving access to the population to such a technology, because we neither have the resources to chase down every single region of interest in a scan, nor do we have efficacious treatments for everything we might come across on a scan. Which is why we've settled on scanning things if there are other signs of disease, and only treating something when it significantly impairs life quality and/or expectancy.
Should such a quick and easy scan be in every hospital and research center? Yes. Should it be a spa for people to go to whenever they feel like? No.
I understand the argument but imagine if it were applied to other nascent technologies like the microscope, which incidentally was also viewed with suspicion by doctors who (accurately) cited flaws in early models such as chromatic and spherical aberration. Thankfully, many people persisted in developing it including non-medical polymaths like Robert Hooke. I recognize this may cause some headaches for doctors dealing with insistent patients but I doubt it will be a permanent problem as the technology develops further and becomes more widespread.
"the people can't be trusted with knowledge" is a bad argument
we don't need to do much differently to take advantage of this data anyway. doctors already ask patients what changed recently
collect data passively. when a medical condition arises, you have a data source to correlate against the onset of the condition
currently we have almost no data, so doctors need to run multiple tests to identify possible causes
> we don't need to do much differently to take advantage of this data anyway. doctors already ask patients what changed recently
So your take is we just do the testing and ignore it's outputs entirely, until something comes up? And that is somehow different and better than current imaging processes?
> currently we have almost no data
This is absolute fucking nonsense.